Multilayer laminates

Laminates (multilayer structures), where each layer itself may be either a single-phase material or a multiphase material [10]. Examples of laminates include some electronic components, many structural composites, adhesive joints, and any other fabricated article where a coating layer (such as an anticorrosion coating or paint) is deposited on another material. See sections 7.C and ll.C.S.d for earlier discussions of such structures in this book. 

The casting onto polymer carriers was first described by Park in 1961 [26]. Tapes are cast in uniform thicknesses, typically based on English units. For example, tapes as thin as about 0.002 in. and as thick as 0.025 in. are in commercial production. Thicker tapes, for example, 0.040 in., have also been demonstrated, although it is difficult to punch and laminate multilayer structures with such tape. In the casting process, control of tape thickness, belt speed, temperature, and drying atmosphere is critical [27]. 

Takahashi, Akio, Thin Film Laminated Multilayer Wiring Substrate, 77PC Proceeding, Vol. 11, No. 7, November 1996, pp. 481-484. 

MAJOR PRODUCT APPLICATIONS bags, film, laminates, multilaye r fiber, sealant, tape, tires, tubing... 

For some applications, more than one polymer layer is desirable. For example, a food tray might need a strong, abrasion-resistant surface layer such as polypropylene combined with an inner layer such as poly(vinylidene chloride) to contribute low oxygen permeability. House siding of poly(vinyl chloride) can benefit from a surface layer of an ABS-type polymer with superior weathering properties. In order to produce laminated, multilayer film by coextrusion, several extruders can be coupled. Each will contribute a separate stream of polymer melt to be combined without mixing in a feed block from which a layered melt issues. Much better adhesion between film layers often can be achieved in this way than could be attained by coating one melt onto a previously extruded and cooled second film. 

Flexible Packaging. Flexible packaging is composed of both single- and multilayer stmctures. The latter may be further subdivided into laminated, coated, and coextmded, or combinations of these. 

Free mono- and multilayer films may be adhesive- or extmsion-bonded in the laminating process. The bonding adhesive may be water- or solvent-based. Alternatively, a temperature-dependent polymer-based adhesive without solvent may be heated and set by cooling. In extmsion lamination, a film of a thermoplastic such as polyethylene is extmded as a bond between the two flat materials, which are brought together between a chilled and backup roU. 

Thermoform able sheet may be mono- or multilayer with the latter produced by lamination or coextmsion. Multilayers are employed to incorporate high oxygen-barrier materials between stmctural or high water-vapor barrier plastics. Both ethylene vinyl alcohol copolymers and poly(vinyhdene chloride) (less often) are used as high oxygen-barrier interior layers with polystyrene or polypropylene as the stmctural layers, and polyolefin on the exterior for sealing. 

Thin-film media can be made by various technologies, eg, sputtered deposited Co—Cr—X films for longitudinal appHcations, laminated media for hard disk apphcation, metal evaporated tape, and multilayers for possible appHcations in magnetooptic recording. 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Many grades of interlayer are produced to meet specific length, width, adhesion, stiffness, surface roughness, color (93,94), and other requirements of the laminator and end use. Sheet can be suppHed with vinyl alcohol content from 15 to about 23 wt %, depending on the suppHer and appHcation. A common interlayer thickness for automobile windshields is 0.76 mm, but interlayer used for architectural or aircraft glaring appHcations, for example, may be much thinner or thicker. There are also special grades to bond rear-view mirrors to windshields (95,96) and to adhere the components of solar cells (97,98). Multilayer coextmded sheet, each component of which provides a separate property not possible in monolithic sheet, can also be made (99—101). 

Layered Structures. Whenever a barrier polymer lacks the necessary mechanical properties for an appHcation or the barrier would be adequate with only a small amount of the more expensive barrier polymer, a multilayer stmcture via coextmsion or lamination is appropriate. Whenever the barrier polymer is difficult to melt process or a particular traditional substrate such as paper or cellophane [9005-81-6] is necessary, a coating either from latex or a solvent is appropriate. A layered stmcture uses the barrier polymer most efficiently since permeation must occur through the barrier polymer and not around the barrier polymer. No short cuts are allowed for a permeant. The barrier properties of these stmctures are described by the permeance which is described in equation 16 where and L are the permeabiUties and thicknesses of the layers. 

Flexible PCBs are produced in large quantities, usually consisting of polyester, polyimide, and polyimide—Teflon films. Both foil-laminated and uncoated versions are available. A modem complex multilayer board after final fabrication is shown in Figure 2. 

Multilayer boards, which use multiple interior laminates of plastic and copper, now comprise over half of the value of production, though much less on a surface area basis. Surface mount technologies demand extreme flatness and reproducibiHty from surfaces. Greater packing density has led to commercial production of finer lines and holes, often less than 50 p.m and 500 p.m, respectively. Electroless gold over electroless nickel—phosphoms, or electroless nickel—boron alone, is often used as a topcoating for wire bonding or improved solderabiHty. 

Current usage is almost entirely associated with the good adhesion to aluminium. Specific applications include the bonding of aluminium foil to plastics films, as the adhesive layer between aluminium foil and polyethylene in multilayer extrusion-laminated non-lead toothpaste tubes and in coated aluminium foil pouches. Grades have more recently become available for manufacture by blown film processes designed for use in skin packaging applications. Such materials are said to comply with FDA regulations. 

Laminated beams (glulam), parallam (or LSL) and fingerjoints a flat pressed multilayer wood beam, thiek wood planks constituting the layers, used for structural exterior applications and bonded with PRF (phenol-resorcinol-formaldehyde) cold-setting resins, or MUF cold-setting resins, or even with certain types of polurethanes (although the use of these latter ones is only established in one country and can show creep and temperature-induced creep problems). The indi-... 

The stress-strain relations in arbitrary in-plane coordinates, namely Equation (4.5), are useful in the definition of the laminate stiffnesses because of the arbitrary orientation of the constituent laminae. Both Equations (4.4) and (4.5) can be thought of as stress-strain relations for the k layer of a multilayered laminate. Thus, Equation (4.5) can be written as... 

Union Carbide Corp produced the first of the synthetic papers in the late 1960s. Since that time other examples of synthetic papers include DuPont s Tyvek nonwoven paper and Van Leer s Valeron cross-laminated film. This market is now dominated by a few large, worldwide ventures with proprietary processing techniques that extend the use of single and multilayer extruded blown film or cast film. 

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